Selective binding and periodic arrangement of magic boron clusters on monolayer borophene.

The synthesis and characterization of small boron clusters with unique size and regular arrangement are crucial for boron chemistry and two-dimensional borophene materials. In this study, together with theoretical calculations, the joint molecular beam epitaxy and scanning tunneling microscopy experiments achieve the formation of unique B5 clusters on monolayer borophene (MLB) on a Cu(111) surface. The B5 clusters tend to selectively bind to specific sites of MLB with covalent boron-boron bonds in the periodic arrangement, which can be ascribed to the charge distribution and electron delocalization character of MLB and also prohibits nearby co-adsorption of B5 clusters. Furthermore, the close-packed adsorption of B5 clusters would facilitate the synthesis of bilayer borophene, exhibiting domino effect-like growth mode. The successful growth and characterization of uniform boron clusters on a surface enrich the boron-based nanomaterials and reveal the essential role of small clusters during the growth of borophene.

Atomistic investigation of surface characteristics and electronic features at high-purity FeSi(110) presenting interfacial metallicity.

Iron silicide (FeSi) is a fascinating material that has attracted extensive research efforts for decades, notably revealing unusual temperature-dependent electronic and magnetic characteristics, as well as a close resemblance to the Kondo insulators whereby a coherent picture of intrinsic properties and underlying physics remains to be fully developed. For a better understanding of this narrow-gap semiconductor, we prepared and examined FeSi(110) single-crystal surfaces of high quality. Combined insights from low-temperature scanning tunneling microscopy and density functional theory calculations (DFT) indicate an unreconstructed surface termination presenting rows of Fe-Si pairs. Using high-resolution tunneling spectroscopy (STS), we identify a distinct asymmetric electronic gap in the sub-10 K regime on defect-free terraces. Moreover, the STS data reveal a residual density of states in the gap regime whereby two in-gap states are recognized. The principal origin of these features is rationalized with the help of the DFT-calculated band structure. The computational modeling of a (110)-oriented slab notably evidences the existence of interfacial intragap bands accounting for a markedly increased density of states around the Fermi level. These findings support and provide further insight into the emergence of surface metallicity in the low-temperature regime.

Moiré-Pattern Modulated Electronic Structures of GaSe/HOPG Heterostructure.

Conventional two-dimensional electron gas (2DEG) typically occurs at the interface of semiconductor heterostructures and noble metal surfaces, but it is scarcely observed in individual 2D semiconductors. In this study, few-layer gallium selenide (GaSe) grown on highly ordered pyrolytic graphite (HOPG) is demonstrated using scanning tunneling microscopy and spectroscopy (STM/STS), revealing that the coexistence of quantum well states (QWS) and 2DEG. The QWS are located in the valence bands and exhibit a peak feature, with the number of quantum wells being equal to the number of atomic layers. Meanwhile, the 2DEG is located in the conduction bands and exhibits a standing-wave feature. Additionally, monolayer GaSe/HOPG heterostructures with different stacking angles (0°, 33°, 8°) form distinct moiré patterns that arise from lattice mismatch and angular rotation between adjacent atomic layers in 2D materials, which effectively modulate the electron effective mass, charge redistribution, and band gap of GaSe. Overall, this work reveals a paradigm of band engineering based on layer numbers and moiré patterns that can modulate the electronic properties of 2D materials.

To compare the influence of blind insertion and up-down optimized glottic exposure manoeuvre on oropharyngeal leak pressure using SaCoVLM™ video laryngeal mask among patients undergoing general anesthesia.

To compare the potential influences of blind insertion and up-down optimized glottic exposure manoeuvre on the oropharyngeal leak pressure (OPLP) in using SaCoVLM™ video laryngeal mask (VLM) among patients undergoing general anesthesia. A randomized self-control study controlled was conducted to investigate the effect of two insertion techniques on OPLP. A total of 60 patients (male or female, 18-78 years, BMI 18.0-30.0 kg m-2 and ASA I-II) receiving selective surgery under general anesthesia were randomly recruited. After induction of anesthesia, the SaCoVLM™ was inserted by blind insertion manoeuvre. The glottic exposure grading(V1) of the SaCoVLM™ visual laryngeal mask and the OPLP(P1) were recorded. And the glottic exposure grading(V2) and OPLP(P2) of SaCoVLM™ were recorded again when the glottic exposure grading was optimal. The glottis exposure grading and OPLP were compared before and after different insertion manoeuver. The glottic exposure grading (V2) obtained by using up-down optimized glottic exposure manoeuvre was better than that obtained by using blind insertion manoeuvre (V1)(P < 0.001). The OPLP was significantly lower in the blind insertion manoeuvre (P1) than in the up-down optimized glottic exposure manoeuvre (P2) (32.4 ± 5.0 cmH2O vs. 36.3 ± 5.2 cmH2O, P < 0.001). In using SaCoVLM™, higher OPLP and better glottic exposure grading were achieved through up-down optimized glottic exposure manoeuvre, protecting the airway while real-time monitoring of conditions around the glottis, which significantly improves airway safety. Our results suggests that up-down optimized glottic exposure manoeuver may be a useful technique for SaCoVLM™ insertion.Trial registration: ChiCTR, ChiCTR2000028802. Registered 4 January 2020, http://www.chictr.org.cn/ChiCTR2000028802.

Comparison of SaCoVLM™ video laryngeal mask-guided intubation and i-gel combined with flexible bronchoscopy-guided intubation in airway management during general anesthesia: a non-inferiority study.

BACKGROUND: When a difficult airway is unanticipatedly encountered and the initial laryngoscopic intubation fails, a supraglottic airway device (SAD) may be placed to aid ventilation and oxygenation, and act as a conduit for intubation. SaCoVLM™, as new SAD, can offer a direct vision to guide intubation. However, no study has evaluated the performance of SaCoVLM™ video laryngeal mask (VLM) intubation and i-gel combined with flexible bronchoscopy (FB)-guided intubation in airway management during general anesthesia. METHODS: A total of 120 adult patients were randomly allocated into the SaCoVLM™ group (Group S) and i-gel group (Group I). After induction of general anesthesia, guided tracheal intubation under direct vision of the SaCoVLM™ was conducted in Group S, while Group I received FB-guided tracheal intubation using the i-gel. The success rate of SAD placement, first-pass success rate of guided tracheal tube placement, and total success rate in both groups were recorded. The time for SAD placement, time for guided tracheal intubation, total intubation time (time for SAD placement and intubation), glottic exposure grading and postoperative intubation complications (i.e., dysphagia, hoarseness, pharyngalgia, etc.) of both groups were also compared. RESULTS: The first-time success rate of SAD placement was 98% in two groups. The first-pass success rate of guided endotracheal intubation was 92% in Group S and 93% in Group I (P = 0.74 > 0.05). The total intubation time was 30.8(± 9.7) s and 57.4(± 16.6) s (95% CI = -31.5 to -21.7) in Group S and Group I, respectively (P < 0.01). The total complication rate was 8% in Group S and 22% in Group I (P < 0.05). The laryngeal inlet could be observed in the S group through the visual system of SaCoVLM™. No dysphagia or hoarseness was reported. CONCLUSION: SaCoVLM™ can reveal the position of laryngeal inlet, thus providing direct vision for tracheal intubation. SaCoVLM™ -guided intubation is faster, and does not rely on FB, compared to i-gel combined with FB-guided intubation. Besides, SaCoVLM™ has a lower post-intubation complication rate. TRIAL REGISTRATION: Chinese Clinical Trials Registry (ChiCTR2100043443); Date of registration: 18/02/2021.

Cortical screw placement with a spinous process clamp guide: a cadaver study accessing accuracy.

BACKGROUND AND OBJECTIVE: The Cortical Bone Trajectory (CBT) technique provides an alternative method for fixation in the lumbar spine in patients with osteoporosis. An accuracy CBT screw placement could improve mechanical stability and reduce complication rates. PURPOSE: The purpose of this study is to explore the accuracy of cortical screw placement with the application of implanted spinous process clip (SPC) guide. METHODS AND MATERIALS: Four lumbar specimens with T12-S1 were used to access the accuracy of the cortical screw. The SPC-guided planning screws were compared to the actual inserted screws by superimposing the vertebrae and screws preoperative and postoperative CT scans. According to preoperative planning, the SPC guide was adjusted to the appropriate posture to allow the K-wire drilling along the planned trajectory. Pre and postoperative 3D-CT reconstructions was used to evaluate the screw accuracy according to Gertzbein and Robbins classification. Intraclass correlation coefficients (ICCs) and Bland-Altman plots were used to examine SPC-guided agreements for CBT screw placement. RESULTS: A total of 48 screws were documented in the study. Clinically acceptable trajectory (grades A and B) was accessed in 100% of 48 screws in the planning screws group, and 93.8% of 48 screws in the inserted screws group (p = 0.242). The incidence of proximal facet joint violation (FJV) in the planning screws group (2.1%) was comparable to the inserted screws group (6.3%) (p = 0.617). The lateral angle and cranial angle of the planned screws (9.2 ± 1.8° and 22.8 ± 5.6°) were similar to inserted screws (9.1 ± 1.7° and 23.0 ± 5.1°, p = 0.662 and p = 0.760). Reliability evaluated by intraclass correlation coefficients and Bland-Altman showed good consistency in cranial angle and excellent results in lateral angle and distance of screw tip. CONCLUSIONS: Compared with preoperative planning screws and the actually inserted screws, the SPC guide could achieve reliable execution for cortical screw placement.

The study of 9,10-dihydroacridine derivatives as a new and effective molecular scaffold for antibacterial agent development.

The emergence of worldwide spreading drug-resistant bacteria has been a serious threat to public health during the past decades. The development of new and effective antibacterial agents to address this critical issue is an urgent action. In the present study, we investigated the antibacterial activity of two 9,10-dihydroacridine derivatives and their mechanism. Both compounds were found possessing strong antibacterial activity against some selected Gram-positive bacteria including MRSA, VISA and VRE. The biological study suggests that the compounds promoted FtsZ polymerization and also disrupted Z-ring formation at the dividing site and consequently, the bacterial cell division is interrupted and causing cell death.

Excessive gestational weight gain in the first trimester is associated with risk of gestational diabetes mellitus: a prospective study from Southwest China.

OBJECTIVE: To evaluate the effects of gestational weight gain (GWG) in the first trimester (GWG-F) and the rate of gestational weight gain in the second trimester (RGWG-S) on gestational diabetes mellitus (GDM), exploring the optimal GWG ranges for the avoidance of GDM in Chinese women. DESIGN: A population-based prospective study was conducted. Gestational weight was measured regularly in every antenatal visit and assessed by the Institute of Medicine (IOM) criteria (2009). GDM was assessed with the 75-g, 2-h oral glucose tolerance test at 24-28 weeks of gestation. Multivariable logistic regression was performed to assess the effects of GWG-F and RGWG-S on GDM, stratified by pre-pregnancy BMI. In each BMI category, the GWG values corresponding to the lowest prevalence of GDM were defined as the optimal GWG range. SETTING: Southwest China. PARTICIPANTS: Pregnant women (n 1910) in 2017. RESULTS: After adjusting for confounders, GWG-F above IOM recommendations increased the risk of GDM (OR; 95 % CI) among underweight (2·500; 1·106, 5·655), normal-weight (1·396; 1·023, 1·906) and overweight/obese women (3·017; 1·118, 8·138) compared with women within IOM recommendations. No significant difference was observed between RGWG-S and GDM (P > 0·05) after adjusting for GWG-F based on the previous model. The optimal GWG-F ranges for the avoidance of GDM were 0·8-1·2, 0·8-1·2 and 0·35-0·70 kg for underweight, normal-weight and overweight/obese women, respectively. CONCLUSIONS: Excessive GWG in the first trimester, rather than the second trimester, is associated with increased risk of GDM regardless of pre-pregnancy BMI. Obstetricians should provide more pre-emptive guidance in achieving adequate GWG-F.

[A Prospective Study of the Relationship Between Dietary Patterns during the Second Trimester of Pregnancy and Gestational Weight Gain].

OBJECTIVE: To study dietary patterns during the second trimester of pregnancy and to investigate the relationship between dietary patterns and gestational weight gain (GWG). METHODS: A prospective cohort study was conducted to select healthy singleton pregnant women at 8-14 weeks of gestation in a maternal and child health care institution in Chengdu city. Food items and quantities were collected at 8-14, 24-28, 32-36 weeks of gestation by using the 3-day 24-hour dietary recall and energy intakes were calculated. Dietary patterns during the second trimester were established by factor analysis and factor scores were calculated. The weight of pregnant women was measured at 8-14, 24-28 weeks of gestation and 1 week before delivery, and the total GWG and the GWG rates in the second and third trimesters were calculated. Multiple linear regression analyses were used to analyze the association between dietary patterns and GWG. RESULTS: A total of 1 004 samples were included. Three dietary patterns were identified: Milk-egg-whole grain pattern, Beverage-dessert pattern and Traditional pattern. The average total GWG was (13.2±4.5) kg. The average weight gain rate was (0.4±0.2) kg/week in the second trimester. The average weight gain rate was (0.5±0.3) kg/week in the third trimester. After adjusting for confounding factors including maternal age, body mass index before pregnancy, dietary energy intake, physical activity, multiple linear regression analysis showed that the factor score of Beverage-dessert pattern was positively associated with the total GWG and the weight gain rate in the third trimester ( ß=0.370, 95% confidence interval ( CI): (0.103, 0.636), P=0.007; ß=0.014, 95% CI: (0.000, 0.027), P=0.049, respectively), and the factor score of Traditional pattern was negatively associated with the total GWG ( ß=-0.285, 95% CI: (-0.555, -0.015), P=0.039). There was no association between the Milk-egg-whole grain pattern and GWG. CONCLUSION: Dietary patterns during the second trimester of pregnancy are associated with GWG. The Beverage-dessert pattern may increase the total GWG and weight gain rate in the third trimester. The traditional pattern may help control the total GWG.

[Associations of Dairy Consumption during Pregnancy and Neonatal Birth Body Mass: a Prospective Study].

OBJECTIVE: To investigate the dairy product intake during pregnancy in Southwest China and to explore its relationship with neonatal birth body mass. METHODS: A prospective study was conducted to select healthy singleton pregnant women at 8-14 weeks of gestation in a maternal and fetal health care institution in Chengdu City. Dairy product consumption during the first, second, third trimester of pregnancy were collected by 24-hour dietary recalls at 8-14 weeks, 24-28 weeks and 32-36 weeks of pregnancy, respectively, and the total milk intake and milk consumption rate were calculated. According to the dietary guidelines for Chinese pregnant women (2016), the recommended amount of milk (300 g/d) was used as the standard to calculate the compliance rate. The respondents were divided into three groups: no dairy consumption group, insufficient dairy consumption group and suitable dairy consumption group. The gestational age at delivery and neonatal birth body mass were collected by the hospital information system. Logistic regression model was used to analyze the association between milk intake during pregnancy and neonatal birth body mass. RESULTS: A total of 962 pregnant women were included. The average milk intake in the first, second and third trimester of pregnancy were 125.0 (0, 236.1) g/d, 208.3 (0, 284.7) g/d and 250.0 (150.0, 416.7) g/d, respectively, with the compliance rates of 12.6%, 33.2% and 48.4%, respectively. The average neonatal birth body mass was (3 225.0±399.8) g. The incidence of small for gestational age (SGA) and large for gestational age (LGA) was 8.3% and 3.9%, respectively. Compared with no dairy consumption group in the second trimester of pregnancy, the risk of SGA was lower in suitable dairy consumption group (odds ratio (OR)=0.786, 95% confidence interval (CI): 0.385-0.976). Compared with no dairy consumption group in the third trimester of pregnancy, the risk of SGA was lower in insufficient dairy consumption group and suitable dairy consumption group (OR=0.672, 95%CI: 0.477-0.821 and OR=0.497, 95%CI: 0.116-0.807, respectively). No association was observed between milk intake in the first trimester and neonatal birth body mass, and milk intake in the second and third trimester of pregnancy was not associated with the risk of LGA. CONCLUSION: Insufficient milk intake of pregnant women is a significant problem in southwest China and needs to be improved. Milk intake during pregnancy is associated with neonatal birth body mass, and increased milk intake in the second and third trimester of pregnancy may reduce the risk of SGA.

Synthesizing Highly Regular Single-Layer Alkynyl-Silver Networks at the Micrometer Scale via Gas-Mediated Surface Reaction.

Extended organometallic honeycomb alkynyl-silver networks have been synthesized on a noble metal surface under ultrahigh vacuum conditions via a gas-mediated surface reaction protocol. Specifically, the controlled exposure to molecular oxygen efficiently deprotonates terminal alkyne moieties of 1,3,5-tris(4-ethynylphenyl)benzene (Ext-TEB) precursors adsorbed on Ag(111). At Tsub = 200 K, this O2-mediated reaction pathway features high chemoselectivity without poisoning the surface. Through mild annealing to 375 K, long-range ordered alkynyl-silver networks incorporating substrate atoms evolve, featuring Ag- bis-acetylide motifs, high structural quality and a regular arrangement of nanopores with a van der Waals cavity of ≈8.3 nm2.

On-Surface Activation of Trimethylsilyl-Terminated Alkynes on Coinage Metal Surfaces.

The controlled attachment of protecting groups combined with the ability to selectively abstract them is central to organic synthesis. The trimethylsilyl (TMS) functional group is a popular protecting group in solution. However, insights on its activation behavior under ultra-high vacuum (UHV) and surface-confined conditions are scarce. Here we investigate a series of TMS-protected alkyne precursors via scanning tunneling microscopy (STM) regarding their compatibility with organic molecular beam epitaxy (OMBE) and their potential deprotection on various coinage metal surfaces. After in-situ evaporation on the substrates held in UHV at room temperature, we find that all molecules arrived and adsorbed as intact units forming ordered supramolecular aggregates stabilized by non-covalent interactions. Thus, TMS-functionalized alkyne precursors with weights up to 1100 atomic mass units are stable against OMBE evaporation in UHV. Furthermore, the TMS activation through thermal annealing is investigated with STM and X-ray photoelectron spectroscopy (XPS). We observe that deprotection starts to occur between 400 K and 500 K on the copper and gold surfaces, respectively. In contrast, on silver surfaces, the TMS-alkyne bond remains stable up to temperatures where molecular desorption sets in (≈600 K). Hence, TMS functional groups can be utilized as leaving groups on copper and gold surfaces while they serve as protecting groups on silver surfaces.

Quantum Tunneling Mediated Interfacial Synthesis of a Benzofuran Derivative.

Reaction pathways involving quantum tunneling of protons are fundamental to chemistry and biology. They are responsible for essential aspects of interstellar synthesis, the degradation and isomerization of compounds, enzymatic activity, and protein dynamics. On-surface conditions have been demonstrated to open alternative routes for organic synthesis, often with intricate transformations not accessible in solution. Here, we investigate a hydroalkoxylation reaction of a molecular species adsorbed on a Ag(111) surface by scanning tunneling microscopy complemented by X-ray electron spectroscopy and density functional theory. The closure of the furan ring proceeds at low temperature (down to 150 K) and without detectable side reactions. We unravel a proton-tunneling-mediated pathway theoretically and confirm experimentally its dominant contribution through the kinetic isotope effect with the deuterated derivative.

Functionalized Graphdiyne Nanowires: On-Surface Synthesis and Assessment of Band Structure, Flexibility, and Information Storage Potential.

Carbon nanomaterials exhibit extraordinary mechanical and electronic properties desirable for future technologies. Beyond the popular sp2 -scaffolds, there is growing interest in their graphdiyne-related counterparts incorporating both sp2 and sp bonding in a regular scheme. Herein, we introduce carbonitrile-functionalized graphdiyne nanowires, as a novel conjugated, one-dimensional (1D) carbon nanomaterial systematically combining the virtues of covalent coupling and supramolecular concepts that are fabricated by on-surface synthesis. Specifically, a terphenylene backbone is extended with reactive terminal alkyne and polar carbonitrile (CN) moieties providing the required functionalities. It is demonstrated that the CN functionalization enables highly selective alkyne homocoupling forming polymer strands and gives rise to mutual lateral attraction entailing room-temperature stable double-stranded assemblies. By exploiting the templating effect of the vicinal Ag(455) surface, 40 nm long semiconducting nanowires are obtained and the first experimental assessment of their electronic band structure is achieved by angle-resolved photoemission spectroscopy indicating an effective mass below 0.1m0 for the top of the highest occupied band. Via molecular manipulation it is showcased that the novel oligomer exhibits extreme mechanical flexibility and opens unexplored ways of information encoding in clearly distinguishable CN-phenyl trans-cis species. Thus, conformational data storage with density of 0.36 bit nm-2 and temperature stability beyond 150 K comes in reach.

[Moderate-to-vigorous Physical Activities and Gestational Weight Gains during the Second and Last Trimesters of Pregnancy].

OBJECTIVE: To determine the level of moderate-to-vigorous physical activities (MVPA) and its relationship with gestational weight gains (GWG) in the second and the last trimesters of pregnancy. METHODS: A prospective study was conducted in Chengdu on 362 healthy pregnant women at the 24-28 gestation weeks who delivered a singleton. Demographic data and pre-pregnancy body mass were collected using a questionnaire. Weight gains at the gestation weeks of 24-28 and 32-36 were measured for the first two trimesters and the last trimester of pregnancy. The Denmark self-reported physical activity scale was used for measuring the duration and intensity of physical activities. Multiple linear regression models were established to determine the relationship between MVPA and GWG. RESULTS: The last trimester had lower average daily MVPA 〔(0.76±0.93) h〕 compared with the second trimester 〔(1.61±1.61) h, t=9.056, P<0.001〕. About 74.6% of the participants met the PA recommendations for the second trimester, compared with 60.5% for the last trimester (χ2=16.387, P<0.001). The participants experienced an average GWG of (7.36±3.78) kg during the first two trimesters, and (5.80±2.57) kg during the last trimester, corresponding to a growth rate of (0.30±0.15) kg/week for the first two trimesters and (0.51±0.22) kg/week for the last trimester. Compared with the most inactive group, the participants with medium PA experienced less GWG 〔(5.34±2.91) kg vs.(6.26±2.54) kg, P<0.05〕 and a lower GWG rate 〔(0.48±0.26) kg/week vs.(0.56±0.20) kg/week, P<0.05〕 during the last trimester. Age, gestational week, ethnicity, pre-pregnant BMI, GDM, pre-pregnant smoking and employment were associated with GWG and the GWG rates during the first two trimesters and the third trimester (P<0.05). Compared with the most inactive group, low 〔-0.358(-0.691--0.026)〕 and medium 〔-0.762(-1.486- -0.037)〕 PA were associated with lower GWG during the last trimester. Moderate PA was associated with a lower GWG rate 〔-0.071(-0.133--0.008)〕 after adjustment for gestational age, energy intake, pre-pregnancy BMI and other potential confounders. CONCLUSIONS: Insufficient physical activities are a serious problem in the pregnant women of Chengdu over the last two trimesters. Appropriate MVPA in the last trimester of pregnancy may reduce GWG and GWG rates.

Intermolecular Hybridization Creating Nanopore Orbital in a Supramolecular Hydrocarbon Sheet.

Molecular orbital engineering is a key ingredient for the design of organic devices. Intermolecular hybridization promises efficient charge carrier transport but usually requires dense packing for significant wave function overlap. Here we use scanning tunneling spectroscopy to spatially resolve the electronic structure of a surface-confined nanoporous supramolecular sheet of a prototypical hydrocarbon compound featuring terminal alkyne (-CCH) groups. Surprisingly, localized nanopore orbitals are observed, with their electron density centered in the cavities surrounded by the functional moieties. Density functional theory calculations reveal that these new electronic states originate from the intermolecular hybridization of six in-plane π-orbitals of the carbon-carbon triple bonds, exhibiting significant electronic splitting and an energy downshift of approximately 1 eV. Importantly, these nanopore states are distinct from previously reported interfacial states. We unravel the underlying connection between the formation of nanopore orbital and geometric arrangements of functional groups, thus demonstrating the generality of applying related orbital engineering concepts in various types of porous organic structures.

One-Dimensionally Disordered Chiral Sorting by Racemic Tiling in a Surface-Confined Supramolecular Assembly of Achiral Tectons.

The aggregation of (pro)chiral/achiral molecules into crystalline structures at interfaces forms conglomerates, racemates, and solid solutions, comparable to known bulk phases. Scanning tunneling microscopy and Monte Carlo simulations were employed to uncover a distinct racemic phase, expressing 1D disordered chiral sorting through random tiling in surface-confined supramolecularly assembled achiral 4,4''-diethynyl-1,1':4',1''-terphenyl molecules. The configurational entropy of the 1D disordered racemic tiling phase was verified by analytical modeling, and found to lie between that of a perfectly ordered 2D racemate and a racemic solid solution.

On-surface synthesis of carbon-based scaffolds and nanomaterials using terminal alkynes.

The covalent linking of acetylene compounds is an important synthetic tool to control carbon-carbon bond formation and has been extensively studied for more than a century. Notably, Glaser coupling and subsequently developed refined procedures present an important route for the fabrication of distinct carbon-based scaffolds incorporating units with both sp(2)- and sp-hybridizations, such as carbyne chains, or two-dimensional (2D) graphyne or graphdiyne networks. However, the realization of the envisioned regular low-dimensional compounds and nanoarchitectures poses formidable challenges when following conventional synthesis protocols in solution, which we briefly overview. Now, recent developments in on-surface synthesis establish novel means for the construction of tailored covalent nanostructures under ultrahigh vacuum conditions. Here we focus on the exploration of pathways utilizing interfacial synthesis with terminal alkynes toward the atomically precise fabrication of low-dimensional carbon-rich scaffolds and nanomaterials. We review direct, molecular-level investigations, mainly relying on scanning probe microscopy, providing atomistic insights into thermally activated reaction schemes, their special pathways and products. Using custom-made molecular units, the employed homocoupling, cyclotrimerization, cycloaddition, and radical cyclization processes indeed yield distinct compounds, extended oligomers or 2D networks. Detailed insights into surface interactions such as bonding sites or conformational adaptation, and specific reaction mechanisms, including hierarchic pathways, were gained by sophisticated density functional theory calculations, complemented by X-ray spectroscopy measurements. For the fabrication of regular nanostructures and architectures, it is moreover imperative to cope with spurious side reactions, frequently resulting in chemical diversity. Accordingly, we highlight measures for increasing chemo- and regioselectivity by smart precursor design, substrate templating, and external stimuli. The ensuing preorganization of functional groups and control of side reactions increases product yields markedly. Finally, the electronic band structures of selected cases of novel low-dimensional hydrocarbon materials accessible with the monomers employed to date are discussed with a specific focus on their differences to theoretically established graphyne- and graphdiyne-related scaffolds. The presented methodology and gained insights herald further advancements in the field, heading toward novel molecular compounds, low-dimensional nanostructures, and coherently reticulated polymeric layers, eventually presenting well-defined arrangements with specific carbon-carbon bond sequencing and electronic characteristics. The functional properties of these or other foreseeable scaffolds and architectures bear significant prospects for a wide range of applications, for example, in nanoelectronics, photonics, or carbon-based technologies.

Surface-Guided Formation of an Organocobalt Complex.

Organocobalt complexes represent a versatile tool in organic synthesis as they are important intermediates in Pauson-Khand, Friedel-Crafts, and Nicholas reactions. Herein, a single-molecule-level investigation addressing the formation of an organocobalt complex at a solid-vacuum interface is reported. Deposition of 4,4'-(ethyne-1,2-diyl)dibenzonitrile and Co atoms on the Ag(111) surface followed by annealing resulted in genuine complexes in which single Co atoms laterally coordinated to two carbonitrile groups undergo organometallic bonding with the internal alkyne moiety of adjacent molecules. Alternative complexation scenarios involving fragmentation of the precursor were ruled out by complementary X-ray photoelectron spectroscopy. According to density functional theory analysis, the complexation with the alkyne moiety follows the Dewar-Chatt-Duncanson model for a two-electron-donor ligand where an alkyne-to-Co donation occurs together with a strong metal-to-alkyne back-donation.

Synthesis of extended graphdiyne wires by vicinal surface templating.

Surface-assisted covalent synthesis currently evolves into an important approach for the fabrication of functional nanostructures at interfaces. Here, we employ scanning tunneling microscopy to investigate the homocoupling reaction of linear, terminal alkyne-functionalized polyphenylene building-blocks on noble metal surfaces under ultrahigh vacuum. On the flat Ag(111) surface, thermal activation triggers a variety of side-reactions resulting in irregularly branched polymeric networks. Upon alignment along the step-edges of the Ag(877) vicinal surface drastically improves the chemoselectivity of the linking process permitting the controlled synthesis of extended-graphdiyne wires with lengths reaching 30 nm. The ideal hydrocarbon scaffold is characterized by density functional theory as a 1D, direct band gap semiconductor material with both HOMO and LUMO-derived bands promisingly isolated within the electronic structure. The templating approach should be applicable to related organic precursors and different reaction schemes thus bears general promise for the engineering of novel low-dimensional carbon-based materials.